1. Field of the Invention
The present invention relates to a pressure sensor and method for manufacturing the same.
2. Discussion of the Related Art
Heretofore, there has been known a pressure sensor which is provided with a pressure housing having a pressure chamber inside and also having a pressure sensitive element (sensor chip) arranged in the pressure chamber, and a joint housing having formed therein a fluid passage for leading fluid serving as a measured object into the inside of the pressure housing. In the pressure sensor of this kind, it is general that the pressure sensitive element is arranged in the pressure chamber partitioned by a diaphragm and that the pressure chamber is filled up with a pressure conveyance medium (silicon oil or the like). Thus, a pressure at which the fluid led into the pressure housing pressures the diaphragm, that is, the pressure of the fluid is conveyed to the sensor chip through the pressure conveyance medium filled up in the pressure chamber.
However, in the foregoing construction, where a potential difference arises between the pressure housing and the pressure sensitive element, dielectric polarization is brought about in the pressure conveyance medium filled in the pressure chamber, whereby the measuring accuracy is liable to be deteriorated. As one for solving the problem, there has been known a pressure sensor wherein a pressure housing and a joint housing are electrically insulated by the interposition of an insulating member therebetween, as described, for example, in Japanese Unexamined, Published Patent Application No. 2004-37318. By taking this construction, it can be realized to prevent the dielectric polarization of the pressure conveyance medium and hence, to perform the pressure measurement accurately.
By the way, it is general that the pressure housing and the joint housing are made of metal material such as stainless steel, brass or the like, and it is usual that brazing with silver solder or the like is used for joining the both members through the insulating member. However, because the pressure housing and the joint housing (both made of metal material) largely differ in thermal expansion coefficient from an insulating member (made of ceramics), a stress attributed to the difference in thermal expansion coefficient is imposed on a joint section therebetween in the course of a high temperature heating step and a subsequent cooling step for the braze jointing. This stress and a residual stress are liable to cause drawbacks such as the breakage of the insulating member or the deterioration of the strength in the jointing.